1. Field of the Invention
This invention relates generally to an automatic focusing apparatus and, more particularly, to an automatic focusing apparatus comprising both a sonar rangefinder and rotatable lens disc in which a specially timed control signal as determined by the rangefinder is utilized to stop the lens disc of the appropriate focal position.
2. Description of the Prior Art
Ultasonic ranging systems are well known for cameras, and in each of the systems ultrasonic energy is transmitted toward a subject to be photographed and the subject reflects the ultrasonic energy back to the camera. Characteristics of the transmitted and received signals may be compared to derive a control signal representative of the subject distance. The control signal can be thereafter used to drive the lens mount of the camera to a position corresponding to the subject distance whereby the subject will be in focus.
U.S. Pat. No. 4,199,246 entitled "Ultrasonic Ranging System For A Camera," by J. Muggli, issued in common assignment herewith, provides an ultrasonic ranging system for a camera having a lens mount movable to a position at which a subject being photographed is in focus. The system includes an ultrasonic transducer that responds to a keying pulse by transmitting a relatively short burst of frequency modulated ultrasonic energy and a synchronized receiver for processing an echo signal produced by the transducer upon receipt of an echo upon a predetermined time interval. The receiver produces a range signal with a characteristic related to the distance of a subject being photographed from the camera. The range signal representing the subject distance may thereafter be used in a manner as is more fully disclosed in U.S. Pat. No. 4,199,244 entitled "Automatic Focusing Camera," issued Apr. 22, 1980, in common assignment herewith to control a gated pulse generator in a nonlinear manner such that the latter produces a train of pulses whose number is representative of the actual position of the lens mount at which the subject will be in focus, and includes a focusing mechanism having means responsive to the pulse train produced by the pulse generator means for displacing the lens mount to the proper position. Such systems are complex and expensive since the range signal must be utilized to control a gated pulse in a nonlinear manner to produce a train of pulses whose number is representative of the actual position of a lens mount. The focusing mechanism must then embody a servo-mechanism to respond to the pulses produced by the pulse generator in order to mechanically displace the lens mount to the proper axial position thereby further contributing to the complex nature of such auto focus arrangements.
A simplified automatic sonar controlled focusing apparatus wherein the objective lens movement occurs in an elapsed time interval which is directly correlated to the elapsed time interval between which the sonar ranging signal is transmitted and thereafter received subsequent to being reflected by the photographic subject is more fully described in U.S. Pat. No. 4,167,316 entitled "Sonar Controlled Lens Focus Apparatus," by B. Johnson et al., issued Sept. 11, 1979, in common assignment herewith. The preferred objective lens arrangement comprises a plurality of lens elements mounted for displacement between a plurality of focal positions by a lens holding disc member disposed for rotation about a fixed center axis. The plurality of lens elements are disposed on the lens holding disc member in circumferentially spaced-apart relation with respect to each other about the center axis. Exposure control is provided by a scanning shutter blade arrangement including a pivotally disposed walking beam for imparting counter-reciprocal sliding movement to the shutter blade elements. The walking beam is pivotally disposed to impact upon an actuator member which, in turn, operates by way of a torsion spring to impact upon the lens holding disc member and thereby rotate the lens holding member so as to sequentially move each of the lens elements into the focal position. The lens disc includes a plurality of spaced apart notches disposed in circumferentially spaced-apart relation about the periphery thereof and a lens pawl releasable upon receipt of the sonar ranging signal is provided to move into a respective one of the notches to stop the rotation of the lens disc at the appropriate focal position. If the lens pawl is released and coincidently strikes the outer periphery of the lens disc at the instant that a notch is rotating past, then the lens pawl may bounce off the notch and not stop the rotation of the lens disc at the desired focal position. In addition, the speed of rotation for the lens disc must also be closely correlated to the timing for transmission and receipt of the sonar ranging signals for subjects located at various distances within given distance ranges from the camera.
Therefore, it is a primary object of this invention to provide an automatic sonar controlled lens focusing apparatus with an electronic timing arrangement to allow the lens focus to change at a substantially slower rate than had heretofore been required in order to correlate the speed of the objective lens movement with the times for transmission and receipt of the sonar ranging signals.
It is also an object of this invention to provide an automatic sonar controlled lens focusing apparatus with a lens disc for holding a plurality of circumferentially spaced apart lens elements, a releasable lens pawl for engaging one of a plurality of notches circumferentially disposed about the periphery of the lens disc for stopping the lens disc at the appropriate focal position and means for timing the release of the lens pawl so as to engage the lens disc in the space between a pair of adjacent notches thereby avoiding the possibility of the lens pawl directly striking a notch so as to bounce off.